The present invention relates to a method or apparatus to control a cooling or heating ventilation fan to control indoor conditioned space temperatures, energy efficiency, thermal comfort, and indoor air quality provided by ventilation and space conditioning equipment.
Residential and commercial HVAC system power consumption in the United States accounts for 30% of average summer peak-day electricity loads, 14% of total electricity use, and 44% of total natural gas use, as reported by the US Energy Information Agency Residential and Commercial Energy Consumption Surveys from 2003 and 2009.
Known thermostats control HVAC systems to maintain thermal comfort conditions at a set point temperature typically within a fixed tolerance of plus or minus 1 degree Fahrenheit (° F.) by circulating cool or warm air to a conditioned space. The tolerance is referred to as an operating differential or hysteresis. Some thermostats allow the user to manually adjust the differential from a default differential setting of 1° F. to a different fixed differential setting of either 1.5 or 2° F. If the user manually adjusts the differential it is then fixed until the user manually adjusts the differential again. Thermostats controlling direct-expansion cooling systems typically turn ON the fan at the same time the cool source is energized and turn OFF the fan at the same time the cool source is de-energized. Similarly, thermostats controlling electric, hydronic, and Heat Pump (HP) heating systems typically operate turn ON the fan when the heat source is energized and turn OFF the fan when the heat source is de-energized. Thermostats controlling gas furnaces typically provide a heating signal to the furnace and the furnace fan controller provides a temperature or fixed fan-on time delay after the furnace has been turned ON to allow time to energize the combustion fan and circulate air to clear the combustion chamber prior to igniting the burner. Typical furnace controllers also provide a temperature or fixed fan-off time delay after the furnace has been turned OFF to recover some of the heating energy stored in the heat exchanger. The temperature-based fan delays either use bimetal switches or temperature sensors to turn on the fan when air leaving the heat exchanger is hot or turn off the fan when air leaving the heat changer is cool. Some thermostats provide the user with an option to manually enter a fixed fan-off time delay for cooling or heating.
U.S. Pat. No. 9,534,805 (Matsouka '805) discloses systems and methods for controlling fan-only cooling. A first phase of a first cooling cycle may be initiated in an enclosure using an air conditioning system having a compressor and a fan that passes air over an evaporator coil. The first phase may include activation of the compressor and activation of the fan. A relative humidity may be measured within the enclosure during the first phase of the first cooling cycle. Subsequent to the first phase and in response to the relative humidity being determined to be below a threshold relative humidity of 45 to 60 percent, a second phase of the first cooling cycle may be initiated during which the fan is activated but the compressor is not activated. The Matsouka '805 discloses processor-readable instructions configured to cause one or more processors to receive, from the one or more temperature sensors, measurements of one or more environmental conditions during the second phase of the first cooling cycle; and alter a duration of a second phase of a subsequent cooling cycle based at least in part on the measurements of the environmental condition during the first cooling cycle. The Matsouka '805 a second phase of the first cooling cycle where the fan is activated but the compressor is not activated occurs prior to the cooling system satisfying the thermostat setpoint and terminating the call for cooling. Morever, the Matsouka '805 second phase of cooling does not occur after the cooling system has satisfied the thermostat setpoint and the thermostat has terminated the call for cooling. Furthermore, the Matsouka '805 second phase of cooling is not initiated unless the relative humidity is below a threshold relative humidity.
International Publication Number WO 2013/149160 (Matsuoka 2013) discloses controlling fan-only cooling duration following normal air conditioning operation. Following normal AC cooling, economical fan cooling is used. The duration of the fan cooling period is adjusted based on temperature measurements made during the previous cooling cycle that ended with fan cooling. An expected temperature drop to be provided by fan cooling as well as an expected time to achieve that drop is calculated based on prior measurements of the cooling operating time. The expected values are then used to improve fan cooling for subsequent cooling cycles. In some cases, fan cooling is not initiated unless: (1) a time limit has an elapsed, such that sufficient condensation is allowed to form on the evaporator coil during the first phase, and (2) indoor relative humidity is below a predetermined threshold. Matsuoka discloses de-energizing the compressor early, generally when the thermostat temperature decreases to the cooling setpoint, and continuing to energize the fan until a first thermostat lower maintenance band temperature (LMBT) is reached. Matsouka teaches that if the LMBT is not reached within 2.5 minutes of fan-only operation, then the fan is de-energized.
U.S. Pat. No. 4,388,692 (Jones et al, 1983) discloses an electronically controlled digital thermostat having variable threshold hysteresis with time in discrete steps. In the heat mode when the triac (heat) is turned on, the hysteresis may be 0.5° F., above the set temperature for a predetermined time period (6 minutes) and then decreased to the set temperature until the triac is turned off. When the triac is turned off, the hysteresis is varied to be 0.5° F. less than the set temperature for 6 minutes and then is increased to the set temperature until the triac is turned back on. In the cooling cycle, the threshold hysteresis characteristic is +/−0.5° F. for ten minutes versus the six minutes in heating mode. The Jones '692 patent controls the range of acceptable cycling of the heating and air conditioning systems and defines a maximum acceptable heating cycling rate of 6 to 7 cycles per hour (i.e., 4 to 5 minutes on and 4 to 5 minutes off per cycle) and a maximum cooling cycle rate for an air conditioner of 3 to 4 cycles per hour (i.e., 7.5 to 10 minutes on and 7.5 to 10 minutes off per hour).
U.S. Pat. No. 6,684,944 (Brynes et al, 2004) and U.S. Pat. No. 6,695,046 (Brynes et al, 2004) disclose a variable speed fan motor control for forced air heating/cooling systems using an induction-type fan motor controlled by a controller circuit which is operable to continuously vary the speed of the fan motor during a start-up phase and a shut-down phase of the heating and/or cooling cycle. The controller circuit includes temperature sensors which are operable to control start-up and shutdown of the fan motor over continuously variable speed operating cycles in response to sensed temperature of the air being circulated by the fan. Brynes discloses control of the heater fan motor speeds to low, medium, or medium-high used for heating.
U.S. Pat. No. 4,369,916 (Abbey 1983) discloses a 120 VAC heating or cooling system fan override relay control to immediately start the blower to circulate air when the heating or cooling element turns on and continue to operate the override for a fixed timed interval by a time delay relay after the heating or cooling element turns OFF. U.S. Pat. No. 4,369,916 teaches starting the blower fan instantly when the heating element is turned on and not waiting for the heat exchanger to reach operational temperatures before turning on the ventilation fan at a low speed used for heating.
U.S. Pat. No. 6,464,000 (Kloster 2002) discloses is a temperature controlled device for a two-stage furnace: 1) low fan speed for low heat mode, and 2) higher fan speed for high heat mode. Kloster '000 teaches a two-speed fan for two-stage heating system. The higher fan speed is limited to available heater fan speeds and the high speed is only used for high heat mode.
U.S. Pat. No. 4,684,060 (Adams 1987) discloses a furnace fan control using a separate fan relay not integral to the furnace assembly and a timing circuit receiving a “burner on signal” produced when a thermostat, or some other circuit, senses burner operation and closes (which is delayed until 40 to 180 seconds after thermostat call for heating). The “burner on” signal is generally inaccessible by technicians and cannot be monitored from thermostat or equipment terminals. The thermostat W terminal signal used to measure heat source operational time, is the only signal accessible in a heating system or thermostat that provides a consistent measurement of heating system operational time for different manufacturers and models. The “burner on” time is significantly different from the thermostat W control signal defined from when the thermostat is initiating a call for heating until when the thermostat is terminating the call for heating. When the thermostat calls for heating, the thermostat W terminal control signal is energized followed by a pre-purge inducer blower that operates for 15 seconds or more to circulate air and purge the combustion chamber of gas. The inducer blower closes a pressure switch to energize the hot-surface ignitor and open the gas valve to ignite the burner which takes 17 seconds or more. The trial-for-ignition sequence proves the burner has ignited and takes 7 to 21 seconds or more and flame proving takes 2 seconds or more. The Gas Training Institute cites the following times for proving and starting the “burner on” time by various manufacturers of furnace controllers: Honeywell 90 to 180 seconds, Robertshaw 60, 90 or 120 seconds, White-Rodgers 90 seconds, and Penn-Johnson up to 120 seconds (T. McElwain. 2-28-2011. Troubleshooting Intermittent Ignition Systems for Gas Furnaces and Boilers. Gas Training Institute. pp. 1-6. https://heatinghelp.com/assets/documents/Troubleshooting-Intermittent-Ignition-Systems-for-Gas-Furnaces-and-Boilers.pdf). Therefore, the Adams '060 “burner on time” is significantly different from the duration of time when the thermostat is calling for heating defining a heating system operating time. The Adams '060 patent discloses a fixed fan-off time delay of 2 minutes based on 0 to 2 minutes of burner operation, a fan-off time delay of 2 to 4 minutes based on 2 to 4 minutes of burner operation, and a fixed fan-off time delay of 4 minutes for all burner operational times greater than 4 minutes. The fan-off time delay of the '060 patent is based on the principle that all of the available stored heat in the system is present when the heat exchanger reaches operational temperature (the '060 patent assumes this requires 4 minutes of operation), and no additional stored heat accumulated after the heat exchanger reaches operational temperature. For furnace operation less than 4 minutes, Adams '060 wastes fan energy and causes thermal comfort issues by circulating unwarmed air into the conditioned space before the heat exchanger is hot enough to provide satisfactory operating temperatures. Gas furnaces generally require at least 4 minutes of time for the heat exchanger to warm up and reach an operational temperature unless there is a fault causing short-cycling such as a blocked air filter or cracked heat exchanger. Therefore, the '060 patent '060 effectively only provides a fixed-fan-off time delay of 4 minutes since all furnaces require at least 4 minutes of time to reach operating temperature and store enough heat to support a longer fan-off time delay.
U.S. Pat. No. 5,248,083 (Adams 1993) discloses an adaptive furnace controller using analog temperature sensing to maintain a constant preselected heat exchanger temperature (i.e., 120 Fahrenheit) during operation and operates the fan time delay until a fixed lower heat exchanger temperature (i.e., 90 Fahrenheit) is reached. The adaptive furnace control regulates a controllable valve to adjust burner firing rate, thereby holding heat exchanger operating temperature constant to create constant ON/OFF times based on the previous cycle ON/OFF times of the furnace by regulating circulation blower speed. By increasing blower speeds to shorten “on” times or decreasing blower speeds to increase “on” times, and thereby achieving optimum cycle times.
U.S. Pat. No. 8,141,373 (Peterson et al. 2012) discloses a method of controlling a circulation fan based on a number of different factors such as indoor/outdoor environmental conditions, HVAC schedule period, time of year, or a pseudo random operation. The purpose of Peterson's disclosure is to move air through a controlled space when the HVAC system is not calling for heating or cooling to increase the comfort level of the occupants, or in some cases to increase the indoor air quality by bringing in a fraction of outdoor air.
U.S. Pat. No. 6,708,135 (Southworth et al. 2004) discloses a method for programming a timer to execute timing commands. The purpose of the Southworth '135 method is to minimize the inventory requirements of multipurpose timers by stocking programmable timers, and programming the timer function either before the timer ships or allowing the end customer to configure the timer to the specific end-use requirement. The functions of the timer include delay on make, delay on break, single shot, etc. The functions can be stung together into a complex sequence of switching functions using an ordering table. Once the sequence (operations and operation duration to be preformed) has been programmed into the timer, the timer preforms that sequence exactly the same every time the sequence has been initiated by a trigger. There is no deviation from the programmed operation once the programmer has been removed and the device is connected to a system. None of the timing durations can change, once established, unless the device is re-triggered during a timing function.
ICM Controls, Inc. (www.icmcontrols.com) has manufactured an on-delay control and an off-delay control for HVAC circulating fans for more than 25 years. The ICM fan delay control has a single input and a single output and is connected between the fan “G” terminal of a thermostat and an HVAC fan relay used to energize the HVAC fan, and provides manually-selected fixed-time delays extending HVAC fan operation.
The California Energy Commission (CEC) published report number CEC-500-2008-056 in 2008 titled “Energy Performance of Hot Dry Air Conditioning Systems” (CEC '056). Table 23 on page 65 of the CEC '056 report provides laboratory test measurements of sensible Energy Efficiency Ratio (EER) and savings from a fixed 5-minute fan-off time delay and an end of compressor cycle (i.e., zero) time delay for compressor cycle operation of 5, 10, and 15 minutes. The report describes a fixed fan-off time delay of five minutes provided decreasing sensible EER values of 8.5, 8, and 7.75 for compressor operational times of 5, 10, and 15 minutes. FIG. 48 on page 66 of the CEC '056 report provides test results of packaged unit latent recovery showing sensible EER versus time for tests with a fixed 10-minute fan-off time delay for compressor operation of 30, 5, and 10 minutes and a 20-minute fan-off time delay for compressor operation of 15 minutes. On page 66 regarding the third test at the 55-minute mark, the report states: “It is evident that the longer compressor on cycle requires a longer ‘tail’ to approach the efficiency achieved by the five minute compressor on cycle within a 10 minute ‘tail.’” Graphically extrapolating the “tail” of the third test based on its slope to achieve a 9.6 sensible EER requires a 30-minute fan-off time delay. This might be theoretically possible under adiabatic laboratory conditions, but impossible to achieve under field conditions in actual buildings due to hot attics, duct losses, infiltration, solar radiation, low relative humidity, and outdoor heat conduction through the building shell. The sensible EER is the ratio of total sensible cooling capacity measured in British thermal units (Btu) divided by total AC electric power measured in Watt-hours (Wh). While the CEC '056 report provides information which may hypothetically improve sensible cooling efficiency under adiabatic laboratory conditions, a need remains to optimize sensible cooling performance in actual buildings.
Pacific Gas and Electric (PG&E) Company published a report prepared by Proctor Engineering Group in 2007 titled “Hot Dry Climate Air Conditioner Pilot Field Test,” Emerging Technologies Application Assessment Report #0603 (PG&E '603). Page 23, FIG. 5 of the PG&E '603 report provides the relationship between End of Fan Cycle Sensible EER (energy efficiency ratio) and Compressor Cycle Length (minutes) for fixed 5 minute high speed tail fan-off delay time. Page 23 of the PG&E '603 report disclosed “With a full speed fan used on the tail, the time delay needs to be shorter and needs to respond to the length of the compressor cycle. FIG. 5 shows the End of Cycle Sensible EER below 7 for compressor cycles less than 9 minutes and is negative for some shorter cycles.” Page 23 disclosed sensible efficiency “improvement as the tail length was increased from 1.5 min to 5 minutes” for the unit in Bakersfield, Calif. FIG. 5 provides a scatter plot of “End of fan cycle sensible EER” versus “compressor cycle length (minutes)” for a fixed 5 minute high speed tail fan-off delay time. FIG. 5 shows efficiencies ranging from less than 0 to 16 for compressor cycle lengths of approximately 4 to 14 minutes. Page 24 disclosed “improvement with an increasing tail length up to 10 minutes at low speed and under all conditions” for the unit in Concord, Calif. Page 24 disclosed “0.5 point improvement when the tail was increased from 1.5 minutes to 3 minutes” and the “efficiency advantage declined when the tail length was increased to 5 minutes” for the unit Madera, Calif. Page 24 disclosed the “a 1 point Sensible EER improvement with an extended low speed tail of 10 minutes” for the unit in Yuba City, Calif. Page 26 of the PG&E '603 report disclosed “air conditioners peak and annual performance can be improved by more than 10% with the proper selection of a fan off time delay.” This disclosure indicates the proper selection is of a fixed fan off time delay with a low fan speed to improve performance.
PG&E published a report prepared by Proctor Engineering Group in 2008 titled “Emerging Technologies Program Application Assessment Report #0724, “Hot Dry Climate Air Conditioner Pilot Field Test Phase II” (PG&E '724). This report disclosed an “optimal” fixed time fan-off time delay for specific climate zones. Page 15 of the PG&E '724 report disclosed an “optimal time delay at each site was determined by recording data every minute through a complete air conditioner cycle.” Page 23, Table 8 of the PG&E report '724 discloses an optimal fan-off delay of 7 minutes for Madera, 20 minutes for Yuba City, and 5 minutes for Fresno. Page 15 of the PG&E '724 report disclosed “The optimal time delay at each site was determined by recording data every minute through a complete air conditioner cycle.”
Proctor Engineering Group prepared an unpublished report in 2009 titled “Concept 3 Furnace Fan Motor Upgrade,” (Proctor '009). Page 9, of the Proctor '009 report disclosed “The Concept 3 dry climate mode uses a proprietary algorithm (patent pending) to run the fan at low speed and very low watt draw for the optimal amount of time after the compressor turns off. The time delay is recalculated during every air conditioner cycle as a function of the available cooling capacity remaining on the indoor coil.” The Proctor '009 report does not disclose a method for recalculating the time delay. Nor does the Proctor '009 report provide a method for calculating the quantity of “available cooling capacity remaining on the indoor coil” during every air conditioner cycle. Page 9 of the Proctor '009 report disclosed “FIG. 6 displays laboratory data from Southern California Edison showing the effect of a fan-off time delay on the sensible efficiency of an air conditioner. Four air conditioner cycles are shown: 30, 5, 10, and 15 minutes. The indoor fan was run for 10 minutes following each cycle, and data was recorded each minute.” FIG. 6 displayed on page 10 of the Proctor '009 report provides time series measurements of the sensible Energy Efficiency Ratio (EER) where the fan-off time delay is fixed at 10 minutes for every air conditioner operational cycle of 30, 5, 10, and 15 minutes.
U.S. Pat. No. 5,142,880 (Bellis, 1992) discloses a solid state control circuit for use in connection with existing low-voltage thermostat terminals of a split-system or packaged HVAC system having a refrigerant system compressor and condenser with outdoor fan and an evaporator and gas-fired furnace or electrical heating elements with indoor blower fan. The '880 patent relates generally to systems for increasing the efficiency of Air Conditioning (AC) units by continuing the blower run time for a fixed time period after the compressor is turned OFF. Specifically, the '880 patent discloses an AC control unit comprising a low voltage room thermostat fan terminal, a low voltage compressor relay terminal, a timing circuit means, a sensitive gate triac, and a power triac. The '880 patent also discloses a method for controlling the on-off time of an indoor fan that is controlled by and associated with an indoor thermostat for a room AC system. The apparatus of the '880 patent is not programmable or adaptable. The delay is related to the supply voltage, which varies from system to system. Bellis provides constant current to the triac gates on the order of 6 milliamps. The total current draw is even higher than that when all components are included. Many systems have do not accommodate this much current draw through control relays without causing a humming noise which irritates the user. The Bellis design momentarily de-energizes the relay when switch from thermostat driven fan to his delay, which may cause relay chatter and excessive wear. Bellis does not provide for an override function if the unit fails.
U.S. Pat. No. 5,582,233 (Noto 1996) discloses a device used to extend the fan run time using a family of fixed time delays, and also periodically activates the fan during times the system is not calling for heating or cooling. The '233 patent requires the device to have access to the 24 VAC signals from the AC transformer. This requirement precludes the device from operating using connections limited to the thermostat since most thermostats do not have both the hot and neutral legs of the transformer. Household wiring only provides the hot (red) signal to the transformer.
U.S. Pat. No. 4,842,044 (Flanders et al., 1989) provides a heating and cooling control system that works by energizing a fan or other fluid circulating device to circulate fluid and effect thermal transfer of energy from the fluid to the spaces being heated and by de-energizing the circulating means at a selected time interval after de-energization of the heating and control system. The '044 patent also claims a heating control system comprising a switching means to effect energization of the fluid circulating means, a switching control means that is energizable in response to operation of the control circuit, and an additional circuit means that energizes the switching control means a selected time interval after de-energization of the heating system. The '044 patent is intended to increase the time the fan is turned on after a heating cycle to improve energy efficiency. The device draws power continuously from the gas solenoid through a 680 ohm resistor, and this method has proven to be problematic in practice. Too much current drawn in this way, can cause a humming noise in the gas valve and false operation. The '044 patent also enables the fan relay to activate the blower as soon as the gas valve is activated. This results in cool air being circulated throughout the home since the plenum is not sufficiently warm. Normal heat operation retards the blower until the temperature in the plenum reaches a preset operating temperature. The '044 patent also requires the addition of a relay circuit. This relay must be active the entire time the fan is to be OFF, creating a significant current draw even when the system is in not calling for heating or cooling. The '044 patent also describes fixed delays. It has no way to adapt the fan delay times either by user input or by the compressor run time. The delays provided by the '044 patent are also subject to the variations of the components selected. Additionally, although Flanders touches on the subject of how his invention works when the fan switch on the thermostat is moved from the AUTO position to the ON position, as described, there is no way for the fan to come on when the occupant requests.
U.S. Pat. No. 4,136,730 (Kinsey 1979) teaches of a device that intervenes with the controls coming from a thermostat and going to the heating/cooling system. The '703 patent discloses a fixed upper limit to the time that the compressor or heating source can be activated and then his invention adds additional time to the blower fan. This activity can increase the efficiency of an air conditioner system by allowing a certain amount of water to condense on the evaporator coil and then re-evaporating this water to cool the home. The amount of water collected varies based on the humidity of the ambient air. Having a fixed compressor run time with a fixed blower time can create a less efficient system than the current invention. In many environments, limiting the compressor run time and counting on evaporative cooling to reduce the home's temperature increases the time required to cool the home. In many cases, the desired set point may never be achieved.
U.S. Pat. No. 7,240,851 (Walsh 2007) discloses about a furnace fan timer. The device disclosed in the '851 patent is strictly a timer with a user programmable interval and duration. The device runs continuously in a never ending loop counting down minutes before operating the fan and then counting the minutes to keep the fan activated. The device disclosed in '851 patent is not compatible with air conditioner systems. Most thermostats connect the fan switch to the air conditioner compressor switch when operating in the automatic fan mode. In systems with air conditioners, the device disclosed in '851 patent activates the air conditioner compressor when it turns on the fan. This requires users to turn OFF the circuit breakers for their air conditioner systems when using his device. The device disclosed in '851 patent has two interchangeable wire connections.
U.S. Pat. No. 2,394,920, (Kronmiller 1946), discloses an HVAC thermostat device to control room temperatures using a pair of thermally responsive bimetallic strips mounted within a circular-shaped housing to control space cooling or heating equipment using low voltage signals.
U.S. Pat. No. 7,140,551, (de Pauw 2006) discloses a similar HVAC thermostat device with a simplified user interface and circular-shaped housing to control space cooling or heating equipment using low voltage signals.
European Patent EP0830649 B1 and U.S. PCT/US1996/009118 (Shah 2002) disclose an adaptive method for a setback thermostat using the intersection of the space temperature with a sloped recovery temperature line which approximates the change in temperature as a function of time during recovery of the temperature controlled space from a setback temperature, to determine the time at which recovery to the occupancy temperature should begin. The '118 PCT application computes and updates the slope of the temperature recovery line based on the time between actually achieving the desired next set point temperature and the next set point time associated with the next set point. If the space heating or cooling load changes, recovery starts at a time more compatible with the current heating or cooling load in order to complete recovery at or near the desired time.
U.S. Pat. No. 4,172,555 (Levine 1979) discloses a thermostat controller system for a building heating and/or cooling system including a stored program of desired temperatures which are to be attained within the building at predetermined times within a repetitive time cycle. The '555 patent discloses a method to determine the optimum time to turn on the heating and/or cooling system to meet the next programmed temperature by turning the system on and then off for a short period of time and the temperature change which results in the building as a result of the transient operation is measured. The time at which the furnace must be switched on to attain the next programmed temperature is then determined as a function of the rate of temperature change as determined by the transient switching and the difference between the instantaneous and the future programmed temperature.
Based on the prior art a need remains to practically optimize sensible cooling and heating performance in actual buildings.